Electrostatic capillary apparatus for producing an imprint

ABSTRACT

A method of and an apparatus for producing an imprint on a recording carrier by providing capillary media, supplying writing liquid in the capillary media, positioning a recording carrier in close spaced proximity to the capillary media, and causing displacement forces to occur by the application of a voltage across the capillary media. The steps result in the electrokinetic movement and discharge of the writing fluid from the capillary media onto the recording carrier.

United States Patent 1 1 Bettin 1 Aug. 7, 1973 ELECTROSTATIC CAPILLARY 3,052,213 9 1962 Schaffert l0l/DlG. 13 APPARATUS FOR PRODUCING AN 3,096,198 7/1963 Schaffert lOl/DIG. l3 IMPRINT 3,177,800 4/1965 Welsh 101 1 3,296,624 l/l967 ASCO" 346 140 [75] Inventor: l-lubertus Bettin, Braunschweig, 3,3 9,566 12/1967 c 3 6/l40 Germany 7 3,582,954 6 1971 Skala 101/1 x 3,673,601 6/1972 Htfl'tZm. 346/75 1 Assigneel y p Werke 3,683,212 8/1972 Zoltan 346 140 x Wilhelmshaven, Germany Filed: Jan. 19, 1972 Appl. No.: 219,107

Foreign Application Priority Data Feb. 5, 1971 References Cited UNITED STATES PATENTS Germany P 21 05 373.6

2/1960 Hollmann 346/75 X Primary Examiner-Edgar S. Burr Attorney-George H. Spencer. Jay- M. Finkelstein et al.

[57] ABSTRACT A method of and an apparatus for producing an imprint on a recording carrier by providing capillary media, supplying writing liquid in the capillary media, positioning a recording carrier in close spaced proximity to the capillary media, and causing displacement forces to occur by the application of a voltage across the capillary media. The steps result in the electrokinetic movement and discharge ofthe writing fluid from the capillary media onto the recording carrier.

8 Claims, 5 Drawing Figures PATENTEDMIS' 1 ms 3,750,564

SHEEI 1 OF 3 Fig. 5 42 Fig', SIGNAL a a a :e: at ua'aoe'e":

SHEET 3 BF 3 PAH-INTEL Ass 7 I975 SIGNAL SOURCE 31 ELECTROSTATIC CAPILLARY APPARATUS FOR PRODUCING AN IMPRINT BACKGROUND OF THE INVENTION This invention relates to a method and apparatus for producing a visible imprint on a recording carrier. The present invention, more particularly, relates to a method and apparatus for producing a visible imprint on a recording carrier by means of a liquid which travels through capillary media in an electrokinetic manner, the media being in fluid communication with a liquid reservoir.

German Published Patent Application No. 1,498,264 discloses an apparatus for recording electrically information which includes a recording carrier roller driven by a motor, a spindle driven by the same motor and having a threaded portion on which an ink writer and a reservoir of ink are arranged to be movable in the recording direction, and a signal generator. The roller and the ink writer simultaneously serve as electrodes. The ink writer contains a capillary portion which ends before the writing tip, and a non-capillary tip which is in continuous contact with the recording carrier.

The ink forms an ink meniscus in the capillary portion and the surface tension of the ink in the meniscus is overcome by the onset of an appropriate control signal so that ink begins to flow out of the capillary portion. The ink meniscus reforms upon interruption of the control signal. The recording carrier employed has an electrical resistance of preferably 1,000 ohms per centimeter and a smooth insulating surface..The pen of the ink writer produces a pressure force of at least 23 pounds between the ink writer and the recording carrier. The pen includes a tip provided with a precious stone or a hard metal which serves to confine the capillary effect to that portion of the ink writer which is not in contact with the recording carrier as well as to reduce frictional wear.

The applied signal voltage attains values of the order of 1,500 volts which require appropriate insulation of voltage-carrying parts. This high signal voltage is necessary to overcome the surface tension of the ink at the ink meniscus and to bridge the non-capillary portion of the ink writer as well as the resistance of the recording carrier. The contact of the ink writer with the recording carrier, which is continuously under contact pressure, requires a hard tip for the ink writer. It is moreover necessary'to repeatedly readjust the ink writer. A further disadvantage is the necessity of using recording carriers not readily commercially available which leads, together with the above-mentioned drawbacks, to an expensive procedure regarding procurement, use and maintenance.

ln a further publication, German Patent No. 1,126,422, a visible imprint recording method and apparatus have been disclosed which utilize a stream consisting of electrically charged particles for writing characters, letters and numerals, the stream being formed in the free air at a distance of a few centimeters from the recording carrier and controlled by an electrical field to impinge on a surface of the recording carrier. The apparatus for performing this method substantially includes a body of insulating material which is provided with a tube for the conduction of liquid, one end of which is connected with a liquid reservoir, the other end facing the surface of the recording carrier which is to receive ink. The end of the tube facing the inkreceiving surface of the recording carrier is designed as an opening so that the stream can be influenced by four deflection electrodes supplied with control voltages. The above-mentioned tube has a capillary effect where the level of the liquid in the liquid container must be set to a fixed value to produce a liquid meniscus in the capillary tube. A roller for holding the recording carrier as well as the capillary tube form electrodes supplied with a potential difference of 4000 volts while voltages up to 1,700 volts are applied to the deflection electrodes.

A substantial disadvantage of this known method, already described in connection with the discussion of the earlier mentioned prior art example, is the complicated design of the voltage-carrying components, particularly since in this prior art apparatus there is the added arrangement and design of required electrostatic components. A further drawback is the maintenance of a fixed liquid level in the supply container which requires an additional control for the ink flowing into the reservoir. A stream of ink required for writing perfect characters depends on the voltages, the distance from the nozzle to the roller, the diameter of the discharge opening cross section, the viscosity of the ink and the surface tension of the ink so that this is possible only with complicated, highly accurate instruments. A further disadvantage of the last-mentioned method and the apparatus for performing it is that characters and letters produced therewith are larger than those produced with conventional implements for writing and printing.

SUMMARY OF THE INVENTION lt is an object of the present invention to provide a method for producing an imprint on a recording carrier in which writing liquid is transferred to the carrier by electrokinetic movement. 7

It is another object of the present invention to provide an apparatus for producing an imprint on a recording carrier which is free of a writer which applies force to the recording carrier.

1t is a further object of the present invention to provide an apparatus for producing an imprint on a recording carrier which operates at relatively low voltages.

It is an additional object of the present invention to provide an appartus' for producing. an imprint on a recording carrier which is free of a hard writing tip.

It is still another object of the present invention to provide an apparatus for producing an imprint on a recording carrier which is inexpensive and simple.

It is still a further object of the present invention to provide an apparatus for producing an imprint on a recording carrier which may readily produce letters, numerals and the like which are of sizes corresponding to those produced by conventional writing and printing implements.

The above-mentioned objects, as well as others which will be clear from the text which follows, is accomplished by providing a method which includes the steps of providing capillary media, supplying writing fluid in the capillary media, positioning a recording carrier in close spaced proximity to the capillary media, and causing displacement forces to occur by the application of a voltage across the capillary media. The application of the voltage causes electrokinetic movement and discharge of the writing fluid from the capillary media onto the recording carrier.

The above-mentioned objects, as well as others which will become apparent from the text below, are also accomplished by providing an apparatus having capillary media and a source of writing fluid for supplying fluid in the capillary media. Electrodes are coupled to the capillary media and means are provided for positioning a recording carrier in close spaced proximity to the capillary media. A signal source is coupled to the electrodes for supplying a voltage across the capillary media.

It is a characteristic of the present invention that displacement forces occurring in writing liquid cause a discharge of the writing liquid from capillary media upon the application of an electrical voltage to the capillary media provided with electrodes of opposite polarity so that the writing liquid is transferred to a recording carrier.

In an advantageous apparatus embodiment of the present invention, thin capillary tubes are used which cooperate with the surface of a recording carrier with one of their two openings, electrodes being associated with the first opening and second opening.

Another advantageous apparatus embodiment permits the use of the method according to the present invention in the copying art. Instead of the previously employed electrophotographic image transmission device, the method and apparatus of the present invention can be employed.

The advantages obtained with the present invention can be seen particularly in that a relatively low voltage is applied to the electrodes to control the writing liquid so that the electrical components required for practicing the method and in the apparatus of the present invention can have smaller dimensions. The electric potential amounts, for example approximately 12V, if the capillary channel is mm long with a transverse section of 0.2mm. The movement of ink is dependent on the dielectric constant between the capillary channel and the ink, the electricfield, the electric potential and the viscosity of ink.

The size of the characters, letters, numerals and the like produced with the apparatus of the present invention corresponds to the size produced by conventional implements for writing and printing.

Another advantage of the present invention is the direct transmission of the ink to the recording carrier since the airgap between the exit opening of the capillaries and the recording carrier of the apparatus is kept so small mechanically that only a slight contact between the discharged writing liquid and the recording carrier takes place and no frictional wear occurs on the capillary media. Commercially available papers can be used, even those with low absorption, since the direction of the ink flow can be reversed in fractions of a second simply by a change in the polarity of the voltage between the electrodes.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view of an apparatus for producing an imprint on a recording carrier con structed according to the present invention, a liquid filled capillary tube and electrodes being shown in section.

FIG. 2 is an illustration ofa second apparatus for producing an imprint on a recording carrier according to the present invention, a liquid filled capillary chamber,

ink chamber and electrodes being shown in section along line 2-2 of FIG. 3.

FIG. 3 is a partially broken open plan view of the apparatus shown in FIG. 2.

FIG. 4 is a partially cross-sectional perspective view ofa third embodiment'of an apparatus according to the present invention.

FIG. 5 is a partially broken open plan view illustrating a fourth embodiment according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The phenomena on which the present invention is based, sometimes referred to as electro-osmosis, is well known in the electrochemical field. As described in Lueger, LEXIKON DER TECHNIK, Volume 2, page 124, Alfred Erhardt and Hermann Franke, published by DEUTSCHE VERLAGS-ANSTALT, Stuttgart, W. Germany (1960), water in a capillary glass tube is normally charged positively with respect to the wall of the glass tube. When an electrical voltage is applied, the water moves toward the cathode since the forces exerted on the ions by the electrical field are transferred to the liquid by friction. Liquids with the opposite polarization phenomena therefore move in the opposite direction. It has now been found through appropriate experiments that the displacement forces occurring in the liquid are directly proportional to the current intensity. According to the present invention this phenomena is utilized in a method and an apparatus for producing visible imprints.

Referring to FIG. 1, a capillary tube 1, which may be made of glass, receives a writing liquid which is replenished from a reservoir 2 and which is charged in the capillary tube 1 by the electro-osmosis phenomena as described above. This phenomena is diagrammatically illustrated in FIG. 1 by the small circles with positive and negative signs. When a voltage of one polarity from a signal source 9 is applied across electrodes 3 and 4 the liquid moves, in the direction of arrows 8, as a consequence of the displacement forces occurring in the liquid, toward the electrode 4 where a liquid meniscus 7is formed at a discharge opening 6 facing a recording carrier 5. The liquid is transferred to the recording carrier 5. By changing the polarity of the voltage, supplied to the electrodes 3 and 4 from the signal source 9, the liquid is moved in the direction opposite to the direction shown by the arrows 8 so that after the imprint of the character on the recording-carrier 5 the liquid can be moved back by fractions of millimeters and the printed character will not be smeared by an excess of liquid. The electrodes 3 and 4 are coaxially arranged at opposite ends of the capillary tube 1 and are provided with apertures for the passage of ink of the size of the inner diameter of the capillary tube 1. Commercially available inks can be used which also have the opposite polarity behavior than that described, i.e., which charge negatively compared to the glass wall of the capillary tube 1.

A second embodiment of an apparatus according to the present invention for producing a dot-type script is shown in FIGS. 2 and 3, FIG. 2 being a sectional view of FIG. 3 taken along the line 2 2. In FIG. 3 a portion of the housing is broken away which would otherwise cover ink-filled chamber 10, electrodes ll, 12 and 13 and partitions 14. The electrode 11 is disposed in the ink-filled chamber without being in contact with capillary chambers 19 which are arranged according to a dot pattern in the direction of the line to be written. The electrode 11 is held by electrically insulated end walls and 16 and may have a bore for the replenishment of ink, which is not shown, this bore being in flow communication with a reservoir, also not shown, similar to the reservoir 2 shown in FIG. 1. The electrodes 12 and 13 have the same polarity and amplitude of voltage, supplied from a signal source 17, and define the capillary chambers 19 together with one of a plurality of electrically insulating partitions 14 and the wall 15 or the wall 16, or with two of the partitions 14. These capillary chambers 19 are in flow communication with the ink chamber 10. The ink chamber 10 is closed off by a curved electrically nonconductive housing portion 22. The electrodes 13 disposed downstream relative to the direction of movement, diagrammatically shown by arrow 18, of a recording carrier 20 are shortened by tenths of millimeters so that an opening 21 is formed andonly the electrodes 12 are disposed in the imprint range of the recording carrier 20. Smearing of the ink on the recording carrier 20' is thus avoided. When a voltage pulse, of one or the other polarity, from the signal source 17 is applied to the electrodes ll, 12 and 13, the ink contained in the capillary chambers 19 is moved as a consequence of the electro-osmotic phenomena described in connection with FIG. 1 so that the fluid is respectively either discharged from the opening 21 or flows in the opposite direction.

FIG. 2 showsthe connectionof signal source 17 to a single pair of opposedelectrodes 12 and 13. associated with one capillary chamber 19. The source 17 is provided with a plurality of separate outputs each connected to one such electrode pair and each conducting an individually controlled output signal-to cause the flow of ink from each capillary chamber to be individually controlled and thus to permit the row of capillary chambers 19 to produce'any desired dot pattern as the carrier 20 moves past-the opening 21.

As illustrated in FIG 4, a third embodiment of an apparatus according to the present invention includes a hollow cylinder23 made of a porous material and arranged to be rotatable in the direction of the arrow 24. The porousmaterial forms in effect a-plurality of capillary pores. The hollow cylinder 23 is closed'with caps 25 and 26'to form a tight 'seal. Bores 28 and 29, for ac commodating an-electrode 27, are provided respectively in the'caps 25 and 26. An ink supply from a reservoir (not shown) can be provided through apertures (not shown) in one of caps 25or 26 or in the electrode 27 whichsimultaneously acts as a drive shaft. On a generatrix of surface 30 of the hollow cylinder 23 a plurality of electrodes 31 are so arranged, i.e., spaced according to the dot-type script to be written, that they are pressed against the surface 30 by resilient members (not shown) either mechanically or electrically. Ink leaves the capillary pores when the ink, which has been polarized in the capillary pores of the hollow cylinder 23 through the application of current pulses from a signal generator 32, moves as a result of the occurring displacement forces resulting from the electro-osmosis phenomena described in conjunction with FIG. 1. The ink leaves the capillary pores only in the area of the electrodes 31.. Each electrode is connected to a separate output of generator 32to receive an individually controlled current signal. To prevent unintended discharge of ink, the surface 30 of the hollow cylinder 23 is impregnated to repel liquids. In order to impregnate cylinder 23, a silicon combined with oil can be used. When the hollow cylinder 23 is rotated by the electrode 27 acting as a drive shaft, the surface 30 and the ink discharged in the area of the electrodes 31 comes in contact with a recording carrier 33 to make an imprint. The electrodes 31 are shown greatly enlarged, for purpose of clarity, and only in principle. It is to be appreciated that many electrodes may be used in practice, and the signal generator 32 may be programed to energize the many electrodes in selected predetermined patterns to effect printing of selected characters, letters, numerals, and the like.

The method and apparatus constructed according to the present invention can be applied in electrophotographic arts and results in an advance in the electrophotographic art. The previously needed and used electrostatic plates or rollers which can be excited by light are replaced, according to the present invention, by capillary media and instead of a device for transferring the toner powder an ink chamber in flow communication with the capillaries of the capillary media is used.

To produce different shades of gray when printing pictures, for example, it is necessary to make the liquid droplets of different relative sizes. An apparatus for accomplishing such printing according to the present invention is shown in FIG. 5. On the surface 34 of a porous hollow cylinder 35 a light-sensitive layer 36 is applied. Experiments have indicated that excellent results are obtained'by forming the light-sensitive layer 36-of cadmium sulfide. If desired, other known light-sensitive materials could be used. An electrically conductive grid electrode37 having square openings is arranged on the light-sensitive layer 36 and serves as electrode. The grid 37 alternatively could be arranged within the light-sensitive layer 36. A counter-electrode 38 is in a cavity 39 filled with ink and is held by two locking caps 40 which seal the hollow cylinder 35 against leaks so that there will be no contact with the porous hollow cylinder 35. The conductive grid 37 as well as the electrode 38 are connected with a signal source (not shown) similar to the signal source 9 shown in FIG. 1. Illuminating the light-sensitive layer 36 causes this layer to become more or less electrically conductive depending on the degree of the intensity of the illumi nation so that the application of a voltage across the electrodes 37 and 38 leads to locally different currents andthus to different displacement forces. The consequerice of the different displacement forces is the release of different amounts of ink' to'th'c surface 34 from the cavity 39 of the porous hollow cylinder 35. The illumination of the light-sensitive surface 36 may be effected photooptically, as for example in the known methods for electrophotographically copying originals.

The recording carrier in FIG. 5 is disposed as in FIG. 4. The electric potential for producing ink-flow is sup plied by contact shoes 41. The grid 37 is a net shaped electrode. It covers a small part of the surface from the layer 36. The layer is available for many copies 42. It is porous to the ink. The axial and radial dimensions of the cylinder 35 amount to approximately 10mm. The wall thickness of the cylinder 35 amount toapproximately 2.5mm. The rotation of the recording carrier is dependent on the motion of the copy 42, because the recording carrier has to roll down about the copy 42 or vice verse.

The four different apparatuses described above are suitable for carrying out the method of producing an imprint according to the present invention. The method includes the steps of providing capillary media, positioning a recording carrier in close spaced proximity to the capillary media, supplying writing liquid to the capillary media, and thereafter causing displacement forces to occur by application of a voltage across the capillary media resulting in electrokinetic movement and discharge of the writing fluid from the capillary media onto the recording carrier.

A preferred more detailed method, according to the present invention includes the further step of reversing the polarity of the voltage across the capillary media resulting in electrokinetic movement of the writing fluid in a direction opposite to the direction causing discharge, the discharge of the writing fluid then ceasmg.

It will be understood that the above description of the present invention is susceptible to various modification, changes and adaptations, and the same are intended to be comprehended within the meaning and range of equivalents of the appended claims.

I claim:

1. Apparatus for producing an imprint on a recording carrier, comprising, in combination:

a. a hollow cylinder of porous material having a cylindrical wall defining capillary media, said wall enclosing a cavity for containing writing liquid and said wall having an outer surface operatively arranged as discharge means for fluid to be transferred to an imprint receiving surface of such recording carrier,

b. means disposed for supplying writing fluid to said capillary media,

c. electrode means coupled to said capillary media and composed of at least one electrode in constant contact with said outer surface and an additional electrode within said cavity free from direct contact with the inner surface of said wall,

d. means for positioning a recording carrier in close spaced proximity to said capillary media; and

e. means electrically coupled to said electrode means for supplying a voltage signal of selected polarity between said additional electrode and said electrode in contact with said outer surface and thus across said capillary media, whereby displacement forces occur resulting in electrokinetic movement and discharge of the writing liquid from the capillary media onto such recording carrier.

2. Apparatus as defined in claim 1 wherein said means electrically coupled to said electrode means is a means for supplying voltage signals of either polarity across said capillary media whereby displacement forces may occur resulting in electrokinetic movement of the writing liquid in either of two directions causing, selectively, the discharge and the ceasing of the discharge of writing liquid from said capillary media.

3. An apparatus as defined in claim 1 wherein said outer surface is impregnated with a liquid-repelling material.

4. An apparatus as defined in claim 1 for producing an imprint corresponding to a light pattern, and further comprising a layer of light-sensitive material disposed on said outer surface of said cylindrical wall to be illuminated by such light pattern and to be subjected to the voltage signal produced between said electrodes, the electrical conductivity of said layer being dependent on light intensity, whereby the ink displacement forces vary across said outer surface as a function of the light intensity pattern across said layer of light-sensitive material.

5. An apparatus as defined in claim 4 wherein said layer is a layer of cadmium sulfide.

6. An apparatus as defined in claim 4 further comprising an electrically conductive guide means in contact with material of said layer.

7. An apparatus as defined in claim 1 wherein there is a plurality of electrodes in contact with said outer surface and said means for supplying a voltage signalcomprises means for supplying voltage signals between said additional electrode and each of said plurality of electrodes.

8. An apparatus as defined in claim 7 wherein said plurality of electrodes are arranged on at least one generatrix of said outer surface, said plurality of electrodes having a spacing which corresponds to the raster denscript.

sity of a given dot-type 

1. Apparatus for producing an imprint on a recording carrier, comprising, in combination: a. a hollow cylinder of porous material having a cylindrical wall defining capillary media, said wall enclosing a cavity for containing writing liquid and said wall having an outer surface operatively arranged as discharge means for fluid to be transferred to an imprint receiving surface of such recording carrier, b. means disposed for supplying writing fluid to said capillary media, c. electrode means coupled to said capillary media and composed of at least one electrode in constant contact with said outer surface and an additional electrode within said cavity free from direct contact with the inner surface of said wall, d. means for positioning a recording carrier in close spaced proximity to said capillary media; and e. means electrically coupled to said electrode means for supplying a voltage signal of selected polarity between said additionaL electrode and said electrode in contact with said outer surface and thus across said capillary media, whereby displacement forces occur resulting in electrokinetic movement and discharge of the writing liquid from the capillary media onto such recording carrier.
 2. Apparatus as defined in claim 1 wherein said means electrically coupled to said electrode means is a means for supplying voltage signals of either polarity across said capillary media whereby displacement forces may occur resulting in electrokinetic movement of the writing liquid in either of two directions causing, selectively, the discharge and the ceasing of the discharge of writing liquid from said capillary media.
 3. An apparatus as defined in claim 1 wherein said outer surface is impregnated with a liquid-repelling material.
 4. An apparatus as defined in claim 1 for producing an imprint corresponding to a light pattern, and further comprising a layer of light-sensitive material disposed on said outer surface of said cylindrical wall to be illuminated by such light pattern and to be subjected to the voltage signal produced between said electrodes, the electrical conductivity of said layer being dependent on light intensity, whereby the ink displacement forces vary across said outer surface as a function of the light intensity pattern across said layer of light-sensitive material.
 5. An apparatus as defined in claim 4 wherein said layer is a layer of cadmium sulfide.
 6. An apparatus as defined in claim 4 further comprising an electrically conductive guide means in contact with material of said layer.
 7. An apparatus as defined in claim 1 wherein there is a plurality of electrodes in contact with said outer surface and said means for supplying a voltage signal comprises means for supplying voltage signals between said additional electrode and each of said plurality of electrodes.
 8. An apparatus as defined in claim 7 wherein said plurality of electrodes are arranged on at least one generatrix of said outer surface, said plurality of electrodes having a spacing which corresponds to the raster density of a given dot-type script. 